Indoor Dipole for Scanner?

[poppafred]

Does anyone have any experience with building a dipole for indoor use on a scanner?

I have a G5RV for my ham station and the reception is great when I hook the scanner up to it. But I would like to have something to use when I am in the living room. I have tried to run a length of coax to the scanner from the ham shack but the signal loss is too great and a telescoping whip is more efficient. Also, thunderstorms dictate disconnecting the antenna from the scanner and that is when I would rely on it the most.

I have all the materials it would take, including a 4:1 balun but don't have a clue on wire length or polarity. I am thinking everything would be vertically polarized but most scanner yagis are horizontal and everyone raves about their reception.

So, any thoughts?

 

[kc2rgw]

I would put a discone in the attic, otherwise the Watson W-889 whip has been pretty amazing for what it is. Unless you went with a much more elaborate antenna it would be hard to beat for the times when you aren't on the outdoor antenna.

For VHF/UHF which is 99% of what I monitor it edges out my RH77 for portable use. The elbow joint on it is great for portables as you can lay the portable down nice and stable on a table with the antenna upright...saves from clumsy dogs and wives .

 

[kb2vxa]

Uh oh, you have a LOT to learn about antennas and radio communications theory in general so I strongly urge you to start cracking the books. Meanwhile get yourself a proper scanner antenna and coax for VHF/UHF work, there is plenty of information to be found on these forums. If you happen to be into 2M and 70cM operation a dual band vertical will do it, the receive is broad enough so I used one for many years with great success. Trouble is most antennas tend to suck raw eggs on 800MHz but that's another can of worms.

Not a put-down or anything but unfortunately you fall into the category of "plug 'n play ham". We OTs or OFs if you prefer, end up elmering you from the ground up because you have learned absolutely nothing about "the fine art of radio" thanks to the FCC having geared the exam requirement to operating practice and left design theory face down in the dust, that knowledge no longer being a requirement for licensing. We don't blame you for lacking education when nobody gave you one in the first place but there is plenty of study material out there and we're willing to help you with it so if you're not a club member already it's a good idea to join. Face to face like in a classroom is always best, remote control teaching is difficult to near impossible which is why you'll learn little on these forums besides having a few questions answered. Step up, step out and learn, you'll be glad you did.

 

[kpoe_28]

This would be a good start for ya, N4UJW ANTENNA DESIGN LAB - Ham Radio Antennas - Design 0r Build Your own Ham Radio Antenna

 

[poppafred]

Uh oh, you have a LOT to learn about antennas and radio communications theory in general so I strongly urge you to start cracking the books.

Why spends hours or days digging through my library of a couple of dozen different antenna and RF propagation books when I can simply ask my question here and hope for a civil answer?

Meanwhile get yourself a proper scanner antenna and coax for VHF/UHF work, there is plenty of information to be found on these forums. If you happen to be into 2M and 70cM operation a dual band vertical will do it, the receive is broad enough so I used one for many years with great success. Trouble is most antennas tend to suck raw eggs on 800MHz but that's another can of worms.

If I wanted a "proper scanner antenna", I wouild reach over in the drawer and pick out one of over a dozen I own intended for handheld radios or hook up one of the FOUR I have mounted outside on the tower.

Not a put-down or anything but unfortunately you fall into the category of "plug 'n play ham".

"Not a put down" but then you call me a "plug 'n play ham". What would you call that? A compliment?

We OTs or OFs if you prefer, end up elmering you from the ground up because you have learned absolutely nothing about "the fine art of radio" thanks to the FCC having geared the exam requirement to operating practice and left design theory face down in the dust, that knowledge no longer being a requirement for licensing.

I didn't ask anyone to be my "elmer". I had a great one 20 years ago (he is now SK) and I seriously doubt you would come anywhere NEAR filling his shoes. I thought it might be fun to play around with a different antenna design and saw no need in duplicating someone else's previous efforts. And, besides, OM's like you are generally referred by a different set of initials. didah didididit

We don't blame you for lacking education when nobody gave you one in the first place but there is plenty of study material out there and we're willing to help you with it so if you're not a club member already it's a good idea to join. Face to face like in a classroom is always best, remote control teaching is difficult to near impossible which is why you'll learn little on these forums besides having a few questions answered. Step up, step out and learn, you'll be glad you did.

Where do you come up with the cajones to take that kind of a slap at someone you do NOT know, who is just asking a simple question? My shack is full of dead bug projects, homebrews and kits. I have several boxes of wire bundles of different lengths left over from all types of LF, MF and HF antenna projects. How do you take a simple question and make the rash assumption that I have no education or training?

And where do you think I got the idea for a possible VHF, UHF, EHF dipole?
A commercial design available from Scanner Master:
WAN-97A Active Nomad Base Antenna

Why buy it if I can build it? Is that concept "old school" enough for you?

Dipoles are inherent in all types of antenna designs for all frequencies. Most yagis use a form of dipole for the radiator, differing the feed slightly. Verticals are simply dipoles using earth ground as a counter poise. Corner reflectors use a dipole as the radiator. TV "rabbit ears" are a form of dipole.

All antenna experiments start with a dipole and modify it in some manner. Resonance, capacitance and resistence are all calculated into the equations to find an efficient design. All I wanted to know if someone else had bothered to start from scratch and was trying to learn from what they had found. I just wanted help with possible wire lengths.

If you do not know the answer or have no experience with the question, DON'T REPLY TO THE POST!!

And stop making assumptions, you come across as arrogant, rude and obnoxious. Your condescending remarks were NOT needed, wanted nor appreciated.

 

[poppafred]

This would be a good start for ya, N4UJW ANTENNA DESIGN LAB - Ham Radio Antennas - Design 0r Build Your own Ham Radio Antenna

Thanks, I will check it out.

 

[kb2vxa]

"Why spends hours or days digging through my library of a couple of dozen different antenna and RF propagation books when I can simply ask my question here and hope for a civil answer?"

Because you'll learn nothing by taking the easy way out as I said. You GOT a civil answer and a boat load of sound advice yet you started in on me in an uncivil manner, shame on you. I shall engage you no further as it's pointless arguing with a stone, especially one who chose to call me a dirty name in Morse.

 

[kpoe_28]

That's were I got the plan's for the 2 Meter Slim Jim Antenna Using 300 Ohm Twinlead....I went through four ST2 scantenna's (wind & ice) then I built a Slim Jim and put it inside of some PVC pipe,Mounted on top of the tower...WOW! runs circles around the ST2 on VHF(140-170) and does really good in the 42mhz and the 460mhz. So I made another for my 2-meter hand held rig got the standing wave down to 1.2:1 across the 2-meter band, Mounted it up about 20 foot working repeaters 30 miles away with 5 watts easy. 73's

 

[charlie12]

Why spends hours or days digging through my library of a couple of dozen different antenna and RF propagation books when I can simply ask my question here and hope for a civil answer?



If I wanted a "proper scanner antenna", I wouild reach over in the drawer and pick out one of over a dozen I own intended for handheld radios or hook up one of the FOUR I have mounted outside on the tower.

"Not a put down" but then you call me a "plug 'n play ham". What would you call that? A compliment?



I didn't ask anyone to be my "elmer". I had a great one 20 years ago (he is now SK) and I seriously doubt you would come anywhere NEAR filling his shoes. I thought it might be fun to play around with a different antenna design and saw no need in duplicating someone else's previous efforts. And, besides, OM's like you are generally referred by a different set of initials. didah didididit



Where do you come up with the cajones to take that kind of a slap at someone you do NOT know, who is just asking a simple question? My shack is full of dead bug projects, homebrews and kits. I have several boxes of wire bundles of different lengths left over from all types of LF, MF and HF antenna projects. How do you take a simple question and make the rash assumption that I have no education or training?

And where do you think I got the idea for a possible VHF, UHF, EHF dipole?
A commercial design available from Scanner Master:
WAN-97A Active Nomad Base Antenna

Why buy it if I can build it? Is that concept "old school" enough for you?

Dipoles are inherent in all types of antenna designs for all frequencies. Most yagis use a form of dipole for the radiator, differing the feed slightly. Verticals are simply dipoles using earth ground as a counter poise. Corner reflectors use a dipole as the radiator. TV "rabbit ears" are a form of dipole.

All antenna experiments start with a dipole and modify it in some manner. Resonance, capacitance and resistence are all calculated into the equations to find an efficient design. All I wanted to know if someone else had bothered to start from scratch and was trying to learn from what they had found. I just wanted help with possible wire lengths.

If you do not know the answer or have no experience with the question, DON'T REPLY TO THE POST!!

And stop making assumptions, you come across as arrogant, rude and obnoxious. Your condescending remarks were NOT needed, wanted nor appreciated.

When I read his reply to you it made me say that's why some people don't want to be hams.
We would have more names for someone like him down here.
Good luck with your ant.

 

[poppafred]

Because you'll learn nothing by taking the easy way out as I said. You GOT a civil answer and a boat load of sound advice yet you started in on me in an uncivil manner, shame on you. I shall engage you no further as it's pointless arguing with a stone, especially one who chose to call me a dirty name in Morse.

Who said I was wanting to learn anything? All I was looking for was what others had found if they had experimented with a short dipole. I got NOTHING from your post except an assault on my intelligence and insults. That is unless "get yourself a proper scanner antenna and coax" is somehow considered to be a proper answer of how I might make a VHF/UHF/EHF dipole. Your "not a put down" was, in fact, a put down. You all too quickly decided I wasn't trained in "the fine art of radio" for some reason.

I started with an old fashioned novice ticket by copying 27 characters in a row at 5 wpm speed. I passed the Tech written, the 13 wpm code, the General written, the Advanced written, skipped the 21 wpm code because the FCC had dropped the requirement and then passed the Extra written.

As far as insults go, at least it was a little covert and in Morse. It really takes chutzpa for someone with a Tech license to call an Amateur Extra a "plug 'n play ham".

 

[FleetAdmiral]

I constructed a dipole antenna a while back and by no means do I consider myself an expert in antenna design so take this with a grain of salt,

The approach I took to my design was part math, part EM theory, and part just toying around.

First of all since dipole antennas are linearly polarized and have no end fire pattern so it can neither receive nor transmit from the ends of the antenna. Typically you mount the dipoles with the wire ends pointing up and down in the z axis such that your nulls are located towards the ground and towards the sky. Conceptually your radiation and reception pattern looks something like a donut on a stick where the stick is the dipole antenna pointing up in the middle. I suppose if you wanted to pick up someone transmitting above your head in the next floor above you might want to mount the dipole in the x or y direction since in the z direction that transmission would be in the dipole null so you can’t receive it.

I say cant receive lightly since we all know that there is a nice boundary between math and the real world that makes things that shouldn’t work sort of work. The concept is you get very high signal losses at the ends I suppose would be the way to phrase it.

anyways,

One thing worth mentioning is dipoles are not frequency independent and in fact they are very frequency selective so your dipole will only work well for one particular frequency. In terms of impedance matching and relative ease of construction and calculation I would recommend creating a disk cone or if you can deal with impedance matching issues at least a folded dipole because the overall results from a dipole are somewhat bleak at least I would think for a scanning application.

That aside, if you want to mess around and create one here is how I constructed mine.

I first started off by taking the frequency, at which I wanted to build the dipole at and I calculated the wavelength by taking the phase velocity of free space and dividing it by the frequency.

aka

Wavelength = (phase velocity)/(frequency)

In the case of the phase velocity of free space most people use 3*10^(8) also known as the speed of light but there is a equation to calculate it and this is a must if you create your own balun.

Also I found that phase velocity is one of those equations that is found easily in a RF book but not so quickly found on Google search and it is defined as

phase velocity = 1/((relative permeability)*(permeability of free space)*(relative permittivity)*(permittivity of free space))^(1/2)

in which

relative permeability is generally 1 for most easy RF related things

permeability of free space is 4*pi*10^(-7)

relative permittivity will vary depending upon the material it is 1 for free space

and the permittivity of free space is defined as 8.854*10^(-12)

Once you know the wavelength of the signal your trying to design a dipole around, typically dipoles are half-wave dipoles because for example if you created a full wavelength dipole the current distribution on the wire at the signal input would be theoretically zero at the middle of the antenna since the current distribution of a dipole is sinusoidal and if you recall a sine function will go to zero at intervals of pi thus at the middle of the antenna the current becomes zero.
so if you use ohms law to look at your input impedance

resistance = voltage/ current

Anything divided by zero approaches a infinite value so in a nutshell your antenna looks like a open circuit to your scanner or transmitter which I suspect might be a bad thing if all the power got reflected hence why full wave dipole antennas are not used.

So the next thing I did was divide my wavelength by 2 to get my total half-wave dipole length and then I divided my total dipole length by 2 to get the individual length of each element of my dipole antenna.

I also subtracted a small amount of space from each individual dipole length to allow for a gap between each dipole element and It has always been recommended to me to make the gap length as small as possible as you will invalidate the current distribution assumption thus getting a unknown impedance if you make the gap too large which could be rather bad.
It is assumed that a dipole antenna will have a input impedance on the order of 73 ohms with some imaginary component thus to reduce the imaginary component trimming back the half wavelength to something slightly below a half wavelength is not a bad idea as it will reduce the imagery component.

After that I cut some wire I mounted my dipole to an insulator which was pvc pipe in my case since metal in the near field would mess up the antenna pattern. Also wire thickness is somewhat important since if you make the wire too thick you once again change the assumed current distribution thus changing the input impedance.

At this point I took some solid wire and created a homemade twisted pair cable to feed my dipole antenna. The reason why I hooked up a twisted pair cable to my dipole antenna rather than coming straight out of the balun was to prevent higher order EM effects from propagating on the antenna since the twisted pair cable only supports TEM propagation thus by feeding the antenna with a short twisted pair wire the antenna should only operate in TEM mode. Some impedance issues with this aspect of my design could arise since separation determines intrinsic impedance of a parallel transmission line, in my case the spacing from the wire insulation twisted together just happened to work out to be near 70 ohms which is around the input impedance of the dipole antenna.
Now whether or not you gain any real benefit from TEM mode only is questionable, in theory higher order effects can be rather troubling if not accounted for but sometimes easy is always better so it’s a personal call really.


After that I took some 75 ohm coax cable and created a balun by first obtaining the relative permittivity of the coax cable which for my cable was polyethylene, I then calculated the wavelength using this permittivity instead of free space.
After that I found the half wavelength of the coax and cut off a piece of coax cable that length. I then connected both the grounds together and the center connections together of the half wavelength coax to the remaining coax cable that would connect to my scanner.

At this point I connected the end of the half wavelength coax to one side of the twisted pair and the other feed coax to the other twisted pair which were connected to my dipole antenna.
Fundamentally I had an antenna upon which one element had an additional piece of coax while the other element of the dipole did not have this additional length. The goal of the homemade balun was to shift the desired frequency by 180 degrees in order to differentially drive the dipole antenna.

One issue with dipole design is impedance matching with a 50 ohm source since the dipole has an input impedance of around 73 ohms which I got around part of the problem by using 75 ohm coax but you still have the reflection loss from the 75 ohm coax to the 50 ohm scanner or whatever your connecting it to. So you could look into stub tuning or impedance transformers to compensate for this problem but in my case the reflection losses were within my acceptable me playing around limits so I dint perform this step.

Upon examining the antenna using a spectrum analyzer and a RF source the results were relatively decent in terms of what you would expect from a dipole antenna.
The pattern around the antenna donut was uniform which is what you would expect. Measurements at end fire top and end fire bottom were as expected almost nothing while measurements between end fire to end fire got stronger near the middle of metaphoric donut.

I found the whole design and construction rather fun but I wouldn’t expect wonderful results after all it isn’t a Yagi-Uda, though you could add a passive reflector and about 5 or so passive directors to the design and presto you would have created a Yagi-Uda.

Outside of this, I by no means claim to be an expert dipole designer, this is simply the approach I tried and it worked so I’m sure there are a million other ways to do this but this worked for me.

Also you might want to check out a free software call NEC which lets you model dipoles and other simple antennas rather easily and see what there radiation patter is.

 

[poppafred]

Several points are a little murky, to say the least.

Anything divided by zero doesn't approach an infinite value, it is zero.

The mathmatics can be simplified into 468/f=1/2 wavelength in feet where f is you target frequency. Or if you wish 234/f = 1/4 wave.

The twisted pair feed: Wouldn't the proximity of the fields on the twisted pair essentially drop the impedence to > 5 ohms?

The use of a half wave length conductor to reverse the phase in the one element would result in a negation of the signal from the other element, in effect, canceling anything being conducted. And you got this to work?

Your balun construction technique doesn't even sound logical. It isn't a balun, its a closed loop.

Wire thickness has no effect. All current is carried by skin effect, basically, the signal is carried on the surface of the wire.

I like to BS a little myself.

But on occasion, I enjoy listening to the work of a master artist.

Please, carry on!

PS: Can't find a copy of NEC that will work with XP

 

[poppafred]

Check that last, I just found the latest version of 4NEC2 and it WILL run on an XP machine after all.

 

[nanZor]

Does anyone have any experience with building a dipole for indoor use on a scanner?

They work very well, although a center-fed dipole may be a bit much to mount indoors when the transmission line should come out at a 90 degree angle for at least a 1/2 wave or more before bending it.

Thus an indoor "twinlead j-pole" (a half-wave antenna like the dipole) fed at the end may be more suitable. You can build or buy them at many places.

While dipoles will work well on the design frequency and the third-harmonic, (ie a dipole cut for 146 mhz might work well up to a point at 438 mhz) the elevation angle on the third harmonic is more or less a cloverleaf with a high look angle. This may or may not be an issue depending on your location and needs.

Of course it will receive other bands it isn't designed for, and may not be very effective on those bands, but it is a start, and may be all that's necessary depending on your listening interests.

I build simple dipoles out of hefty speaker wire or anything else laying around. Tubing? Sure - if I really need it.

The basics to cut a dipole are 468 / f Mhz * VF, where the Velocity Factor takes into account that RF flows slower in wires and surrounding dielectrics than in free space. (Divide this calcuated value in half to get the length of each "pole" of a dipole, where you attach the coax.) Typically coated wires have a VF of around 0.95 or so, whereas twinlead may have anything from .75 to .85 VF. For scanning, it is not that critical.

Pay attention to your coax transmission line loss. You can cut an 800 mhz dipole, but if you run it down the hall and into another room using lossy RG-174, you may not hear anything. Even RG-58 is quite lossy at VHF/UHF, so for many the easiest thing to do is use 75 ohm RG-6 as a first step.

Yes, this is not the perfect setup without impedance matching, element tuning and all that goes with antenna construction. But it WILL get you started - and that's the fun of it isn't it? Incremental improvements are a lot of fun - or one could just shell out the bucks for something already built and not have any fun.

You may want to look at a total compromise antenna, although convenient - the so-called "OCFD" dipole. There are some construction threads here. This compromise might be all that you need.

Most importantly - keep it fun!

 

[FleetAdmiral]

Dividing by zero itself is an undefined number not zero; I think someone wrote a book called zero a dangerous number that shown if you could Winston Church hill would be a carrot. But conceptually consider this

1/.1 =10

1/.01=100

Skip a few steps and make it really small number

1/.00000000001 = 100000000000

So the general pattern is the smaller number you divide by the larger the result you will get thus the limit of the number is infinite hence the impedance skyrockets to an open circuit.

I’m sure there are several simplifications mathematically when it comes to getting the wavelength values for the dipole. But because I had polyethylene in my coax I needed to recalculate the wavelength for polyethylene instead of air and I also had the need to use wavelength and wave number equations elsewhere for other equations that calculated power density.

If you don’t need to do all of the heavy analysis stuff I’m sure a simplified equation probably would be a better solution but I haven’t worked thru to see how that simplification came about so I can’t validate the accuracy of that at least right now if I get a chance ill double check it with the formal equations just to see if it’s a simplification or a approximation since I haven’t seen the derivation.

As far as the intrinsic impedance of the twisted pair, that’s all based upon transmission line theory which there is a nice article at
Transmission line - Wikipedia, the free encyclopedia
And a set of common design equations for twisted pair at
http://www.digikey.com/Web Export/S...2/PDF/GC_CableDesignEquationsBalancedPair.pdf

If you think about it they sale different impedance twisted pair cable cat5 which is rated at 100 ohms over a defined frequency range. I basically just did a homebrew twisted pair cable and got it in the 70ohm range with the wire thickness I had.

Now By shifting the phase of one antenna 180 degrees on one of my dipole elements with that half wave length coax in my balun it won’t negate anything but ensure that the pattern is symmetric since the field lines that are produced by the top dipole match the ones produced by the lower dipole. Try it out in NEC and see what happens since you can add a source that out of phase and see how it affects the pattern.

The balun is a classic Half-Wave Coxial Balun maybe my description of it was rather poor since it was rather late when I wrote it. It looks something like this 4:1 coax balun design.

But fundamentally if you think about it with that balun one element of the dipole has an extra half wavelength of coax to shift the wave 180 degrees out of phase.

Yep your right the signal is carried on the surface of the wire but if you make that wire too thick you’re going to run into the problem of if you have a big thick wire how do you feed the wire to make the current on the surface evenly distributed across that wire. So it’s not so much the signal on the wire that’s the problem it’s the signal on the wire being symmetric. The solution to this problem is found in cone antennas and the wire approximation bowtie antenna since the cone allows a small signal feed at the top such that you can equally distribute the current down the large wire else its anybody’s guess how current will be distributed if you just hooked a cable up to a alumina can size wire how the radiation pattern would look.

Remember everything about dipoles is symmetric else you get a wacky radiation patter that looks like someone took a bite out of a side of the donut.

I got my copy of NEC at 4nec2 antenna modeler and optimizer

And I downloaded Latest 4nec2 default version (5.7.6) and installed then downloaded the 3d viewer so you can see the patterns in 3d which is the 4nec2 3D extension (5.7.6) on the same site.

NEC is kind of fun to play around with you can even do antenna arrays to some extent maybe even a Yagi-Uda though I haven’t tried that

 

[poppafred]

They work very well, although a center-fed dipole may be a bit much to mount indoors when the transmission line should come out at a 90 degree angle for at least a 1/2 wave or more before bending it.

With a quarter wave on 155 mHz only being 19" it shouldn't be a problem. It may become one if I start considering adding VHF Low.

While dipoles will work well on the design frequency and the third-harmonic, (ie a dipole cut for 146 mhz might work well up to a point at 438 mhz) the elevation angle on the third harmonic is more or less a cloverleaf with a high look angle. This may or may not be an issue depending on your location and needs.

Yeah, that was something that I was wondering about.

Of course it will receive other bands it isn't designed for, and may not be very effective on those bands, but it is a start, and may be all that's necessary depending on your listening interests. The basics to cut a dipole are 468 / f Mhz * VF, where the Velocity Factor takes into account that RF flows slower in wires and surrounding dielectrics than in free space. (Divide this calculated value in half to get the length of each "pole" of a dipole, where you attach the coax.) Typically coated wires have a VF of around 0.95 or so, whereas twinlead may have anything from .75 to .85 VF. For scanning, it is not that critical.

I have wondered how the VF would come into play on a receive-only antenna. I had imagined it would be less of a factor but was not sure.

Pay attention to your coax transmission line loss. You can cut an 800 mhz dipole, but if you run it down the hall and into another room using lossy RG-174, you may not hear anything. Even RG-58 is quite lossy at VHF/UHF, so for many the easiest thing to do is use 75 ohm RG-6 as a first step.

I have a 6' section of RG8X I had planned on using. Intend to hang the dipole just along the ceiling line right above the scanner so I should be okay.

Yes, this is not the perfect setup without impedance matching, element tuning and all that goes with antenna construction. But it WILL get you started - and that's the fun of it isn't it? Incremental improvements are a lot of fun - or one could just shell out the bucks for something already built and not have any fun.

Precisely!

You may want to look at a total compromise antenna, although convenient - the so-called "OCFD" dipole. There are some construction threads here. This compromise might be all that you need.

Most importantly - keep it fun!

You know, I had not even thought about one of the OCF dipoles! A "mini-Wini"!

I tried a couple of OCFD's on HF. They are a little difficult to hang on my lot. That was mainly my own fault for trying to put one up that could work 80m. My elmer had a double extended Zep at one point (he had 20 acres) and was working 40m CW QRP with a goal of WAC. He almost made it before he had a stroke and passed away.

I did manage to find a version of NEC that will run on Win XP so that will help with some of the calculations.

Thanks!

 

[nanZor]

You know, I had not even thought about one of the OCF dipoles! A "mini-Wini"!

Here's the quick rundown, although the ocfd is covered in other threads in much more detail:

Grab a 300-75 ohm TV-type transformer balun - the little square ones will do. Attach 4-feet of wire to one of the 300 ohm screw terminals. Attach 18-inches to the other 300 ohm screw terminal. Hang vertically, but run the coax off the 75 ohm port horizontally as much as you can, or at least a few feet. It doesn't matter if the short end is on top or bottom - use whatever is convenient. You could choke it with a ferrite at the feedpoint, but I find this overkill on such a compromise antenna where the braid's common mode is actually part of the antenna. Put it on an analyzer and you'll see plenty of resonant dips all across the bands.

Note that above about 160 mhz or so, the elevation angle starts to rise rapidly, especially at uhf and even more so at 800 mhz - almost straight up. However, in metropolitan areas, or indoors where there are a lot of reflections, this may not be an issue.

This should hold you over until you get the urge to build low-angle dipoles specifically built for the band(s) of interest!

 

[Anerien]

why spends hours or days digging through my library of a couple of dozen different antenna and rf propagation books when i can simply ask my question here and hope for a civil answer?



If i wanted a "proper scanner antenna", i wouild reach over in the drawer and pick out one of over a dozen i own intended for handheld radios or hook up one of the four i have mounted outside on the tower.

"not a put down" but then you call me a "plug 'n play ham". What would you call that? A compliment?



I didn't ask anyone to be my "elmer". I had a great one 20 years ago (he is now sk) and i seriously doubt you would come anywhere near filling his shoes. I thought it might be fun to play around with a different antenna design and saw no need in duplicating someone else's previous efforts. And, besides, om's like you are generally referred by a different set of initials. didah didididit



where do you come up with the cajones to take that kind of a slap at someone you do not know, who is just asking a simple question? My shack is full of dead bug projects, homebrews and kits. I have several boxes of wire bundles of different lengths left over from all types of lf, mf and hf antenna projects. How do you take a simple question and make the rash assumption that i have no education or training?

And where do you think i got the idea for a possible vhf, uhf, ehf dipole?
A commercial design available from scanner master:
wan-97a active nomad base antenna

why buy it if i can build it? Is that concept "old school" enough for you?

Dipoles are inherent in all types of antenna designs for all frequencies. Most yagis use a form of dipole for the radiator, differing the feed slightly. Verticals are simply dipoles using earth ground as a counter poise. Corner reflectors use a dipole as the radiator. Tv "rabbit ears" are a form of dipole.

All antenna experiments start with a dipole and modify it in some manner. Resonance, capacitance and resistence are all calculated into the equations to find an efficient design. All i wanted to know if someone else had bothered to start from scratch and was trying to learn from what they had found. I just wanted help with possible wire lengths.

If you do not know the answer or have no experience with the question, don't reply to the post!!

And stop making assumptions, you come across as arrogant, rude and obnoxious. Your condescending remarks were not needed, wanted nor appreciated.

epic win that guy is a douche

 

[majoco]

Instead of getting everybody's backs up, why didn't you look in the "Building your own Antenna" subsection?

 

[dave3825]

The thread is 9 years old.